Previous caster and camber gauges for the steerable wheels of vehicles comprised either means that were affixed to the floor adjacent the wheel to be gauged, or means which were mounted on the wheel, such as on the rims against the face of the tire, or on the hub. The earliest of these devices comprised plumb bobs, later spirit levels were used, and the more recent devices comprised electronic apparatus and light beams. However, none of these devices could consistently duplicate their measurements even for the same vehicle because weight on the wheels, motion of the vehicle, the amount of air pressure in the tires, the change in direction of the steerable wheels, etc., all affect and change the caster and/or camber angles. No known previous apparatus set a vertical member in the same plane with the turning axis of the steerable wheel, without removal of the steerable wheel and anchoring the device directly to the turning axis, or to the kingpin for the steerable wheel.
Previous toe-in gauges comprised bars that measured the difference in distance between the fronts and the backs of the two substantially parallel aligned steerable wheels, or employed light beams which also were gauged by separate apparatus mounted on or adjacent the rear or non-steerable wheels. No direct comparison was made between the angle of the rear wheel on one side of the vehicle and the steerable wheel on the same side of the vehicle with the same gauge.
Thus the prior art devices measured only the caster, camber and toe-in angles of the steerable wheels themselves, and not these angles with respect to the turning axis of the steerable wheel and the alignment of the non-steerable wheels.